The invention relates to a municipal waste incinerator and more particularly to an improved attachment between a rotary waterwall combustor and the tires upon which it rotates.
Metal plates are presently utilized to attach the rotary combustor barrel to support tires upon which it rotates. There is a tire near each end of the combustor The tires rest on rollers. The weight of the combustor, including the water in the water tubes and the solid fuel within the combustor is carried through the attachments plates to the tires and to the rollers. The combustor is caused to rotate by a drive system, which causes the solid fuel within to tumble and travel along the length of the combustor while burning Rollers support the tires and enable the combustor to rotate. During normal operation, the combustor barrel, which is made of steel boiler tubes interconnected with steel webs, is at elevated temperature of approximately 500.degree. F.. When idle the temperature will drop to ambient, 0 to 100.degree. F. The combustor thus undergoes significant thermal expansion between idle and normal operating conditions. The attachments of the combustor to the tire must accommodate this expansion The metal plates that make the attachment accommodate the expansion by bending in the direction of the radius of the combustor, which is perpendicular to the plane of the plates. The support plates are made thin enough to accommodate the bending without experiencing excessive stress, in the manner of flat springs and are customarily referred to as support springs. It is important for the axis of the combustor to remain in essentially the same position whether it is idle or operating in order to avoid excessive stresses on the piping and fittings that convey circulating water between the rotating combustor and the stationary boiler and pumps that are connected to the combustor.
The problem with the spring support design is it results in an indeterminate structure that cannot be readily analyzed, and a structure that may be subject to fatigue failure that would shorten it useful life. Thermal expansion of the support springs themselves and deformation of the tire under load puts the springs in compression, and this compression together with the load due to bending of the support spring and the weight of the combustor and waste being burned can result in very high stresses, which would be partially cyclic. The analysis of this support system is difficult and unreliable and thus the system is subject to premature failure.